1. Field of the Invention
The present invention relates to the field of electronic devices, and more particularly to physical and electrical connections between electronic devices.
2. Background of the Related Art
As electronic systems grow more powerful and complex, the need for seamless interaction between electronic components takes on increasing significance. Today countless man-hours are dedicated to the design of systems in which diverse components function together flawlessly without a user's giving a moment of thought to the inner workings of the components or to the complex interfacing between them.
This is particularly true in the world of personal computing. A clear example occurs in the everyday situation in which a business person uses a personal computer for the purpose of desktop publishing. Such a user is concerned only with the business task at hand, and has no interest in the precise technical interaction between the base system processor, keyboard, display terminal, and disk drives. Any problem resulting from incompatibility between those components not only causes the user consternation, but also results in loss of productivity and decreased cost efficiency.
One such problem often arises when multiple display devices are connected to a single base processor within a personal computer system. Such a configuration might be used, for example, by a business person making an audio-visual presentation. In that case, one display device might reside physically near the base processor for use by the individual making the presentation, while other display devices might be situated such that the presentation may be seen by a large group of people. No matter the specific application, however, a user of a multiple-display system should not have to be concerned with how, or when, a particular display device is connected to the base system processor. Unfortunately, this is not always so, and multiple-display arrangements often lead to difficulty.
For example, problems can arise in the common situation in which a personal computer user interfaces with the computer by manipulating an electro-mechanical "mouse" to move a corresponding video cursor among various user-selectable menu options projected on a display device. If two or more display devices are connected to the system processor, and each device displays different user-selectable menu options, the user may wish to "drag" an interface component, such as a menu, from one display device to another. Should a display device be disconnected from the processor while that device is actively displaying the interface component, the user may no longer be able to select menu items and the system could be inoperative. Once again, such an occurrence results in lost productivity and may constitute an unacceptable deficiency in an otherwise "user friendly" system.
This problem would be alleviated if means were provided by which the software running on a base system processor for configuring the use interface could be provided information pertaining to the presence or absence of a peripheral display device. If such means existed, then the software could, upon detecting that an active display device had been disconnected, redirect the user interface component to any still-connected display device and remain in a fully operative state. Such a "peripheral device sensor" would provide a user with worry-free connectivity between components and would represent a significant improvement over the prior art. However, because the typical video display device is passive, meaning that it receives an input signal without transmitting information back to the source of that signal, automatic detection of peripheral display devices is not readily achieved. More importantly, prior art approaches to the detection of passive devices prove unsatisfactory in this context.
In some prior art approaches, electronic devices are coupled by means of application-specific connectors that include special-purpose switches or data lines for automated device detection. Thus, the prior art connectors contain hardware or circuitry that is not otherwise necessary for communication between coupled devices, and therefore represents an undesirable expense. While a custom connector for coupling a video display device with a base system processor could be constructed to include device detection circuitry in addition to the simple data and grounding lines required for video signal transmission, development of such a specialized connector is neither practical nor desirable. This is particularly true where the video signal is a composite analog signal that requires a two-line connector such as an RCA jack.
Connectors now used with video display devices are standard across the industry. A change in connector style would require that a new standard be set, and given the vast number of connectors already in use, such a changeover is quite improbable. Even if an industry-wide transition were plausible, it would not be advisable. Today's video connectors are appropriately simple, inexpensive, and easy to use, and the higher production and retail costs that would accompany even a modest increase in connector complexity would be prohibitive. Thus, there is a pressing need for a method and an apparatus by which an electronic device, such as a computer processor, can automatically detect whether or not it is coupled with another electronic device, such as a video display, without requiring that a non-standard, or special-purpose, connector be used.
Another prior art approach uses standard connectors to detect the presence of remote audio devices, such as headphones for example. In this approach, when a remote device is not present, the audio signal is provided to one terminal of a voltage divider, causing the divider to produce a particular output voltage. If a remote devices is connected, the audio signal is disconnected from the divider, causing it to produce a different output voltage. The difference between these two output voltages can be sufficient to be compatible with TTL logic circuitry, e.g., it could be on the order of several volts, and thereby provide useful information to configuration software.
However, this approach is not suitable for use with a signal such as a video signal, for example, which effectively comprises a somewhat random AC signal with a DC offset that causes the entire signal to be positive, e.g., the signal varies in a range of 0-2 volts. Because of the nature of this signal, the voltage divider approach does not produce a sufficiently large enough voltage swing to produce a TTL-level compatible signal.
Accordingly, it is desirable to provide a means by which a monitor or similar device which employs an information signal such as a video signal can be detected without requiring the use of special connector components for such a function.